Synthetic tanning agent and process for preparing same



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FIF83 United States Patent The present invention relates to new synthetic tanning agents and their preparation. More particularly the present invention relates to condensation products of mixtures of dihydroxy-diphenyl sulfones and highly sulfonated bisphenols with formaldehyde, which products are highly superior tanning agents prepared in a novel manner.

It is known according to US. Patent No. 2,174,287 Guthke, September 26, 1939, to use a sulfone and a bis-phenol in tanning procedures. According to this patent, a sulfone solubilized and condensed under pressure and at temperatures above 100 C. with sodium sulfite and formaldehyde is mixed with a bis (hydroxy-phenyl) propane solubilized and condensed with sodium sulfite and formaldehyde at atmospheric pressure and at moderate temperatures. The resulting physical mixture may be applied to leather. It is also known according to Swiss Patent Nos. 246,989 and 252,302 to condense diaryl sulfones with sulfonated bi-phenyls under strongly acidic conditions until reaction is completed or under slightly alkaline conditions. These products are also useful in tanning procedures.

However, the present invention has Brought about novel tanning agents which are not only different in composition from the tanning agents of the prior art, but which are greatly superior to the tanning agents of the prior art. They are useful as retanning agents for chrome tanned leather and as pretanning agents to form shrunken grain effects. These novel agents have good filling properties and are light fast. Leather so treated is very plump and has a very fast and nice grain. Such leather is further characterized by having higher tensile and stitch tear strengths when compared with leather treated with prior art tanning agents.

These novel tanning agents are obtained by condensing a mixture of a dihydroxy-diphenyl-sulfone and a highly sulfonated bis-phenol with formaldehyde. The condensation is carried out in three stages. The first stage involves condensation with formaldehyde in a very weakly alkaline medium, i.e., a pH of from about 8 to about 9 for about 4 to hours. This is followed by a second condensation with formaldehyde in a neutral medium for about 2 to 4 hours. Finally condensation with formaldehyde is concluded in a weakly acidic medium at a pH of about 4 to 5 for about 4 to 5 hours. If desired, the first condensation may be carried out in a weakly acid medium and the third in a weakly basic medium. Throughout these three steps elevated temperatures e.g., from 95 to 105 C. are maintained. Preferably reflux temperatures of the reaction mixture are used. The final product is bulfered to a pH of about 3 preferably with hydroxycarboxylic acids such as glycolic acid and lactic acid.

We have found that our reaction procedures are critical in nature. By using the different pH mediums which bring about different rates of condensation, by introducing formaldehyde at the start of each new condensation stage which insures the presence of the proper amount of formaldehyde in each stage, by using weakly acid and weakly basic mediums and relatively mild temperatures, a product is obtained which is a mixture of a variety of polymerized molecules having different molecular sizes and structures. We have discovered that the character of such product makes it a superior syntan, in fact 'ice superior to the presently known syntans. Moreover, the conditions employed herein make the process very easy to control and to obtain reproducibility of the product.

It would appear that the reaction could be speeded up by using strongly acid and strongly basic mediums and even higher temperatures. However, products with considerably inferior tanning properties are obtained unless our process is followed.

Our sulfones have the following structure HO OH in which R may be H or ---CH;,. Examples of useful sulfones are dimethyl dihydroxy sulfone, dicresyl sulfone, or mixtures thereof. The cresol used in the preparation of dicresyl sulfone may be ortho, meta or para cresol or a commercial grade cresol which contains mixtures of the isomers of cresol. There are various ways to prepare these sulfones and the examples illustrate a preferred preparation. However, the present invention is not limited to any particular preparation. It is only necessary that the preparation used yields the desired sulfone.

The bis-phenol that we use has the following structure HO OH R: Rr-

in R1 is CH3 Ol' --CH2CH3 and R2 is -H or CH Examples of such compounds are 2,2 bis (para hydroxy phenyl) propane and 2,2 bis (para hydroxy phenyl) butane. This material is highly sulfonated, i.e., to about to of the theoretical maximum degree of sulfonation for the disulfonic acid derivative thereof. Preferably it is sulfonated close to about 80%. Since the condensation process calls for weakly acid, neutral and weakly alkaline mediums, the bis-phenol disulfonic acid must be used in its neutralized form. This is obtained by neutralizing the acid with a base e.g., sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. The sulfonated bis-phenol will have the structure where R and R have the same meaning as previously given for the bis-phenol and X is a metal from the alkaline group such as sodium and potassium or it may be the ammonium group. As the sulfonating agents, 98% and 100% sulfuric acid may be used. However, the sulfonation procedure is not critical and any prior art procedure may be employed so long as the proper degree of sulfonation is achieved. Such procedure does not form a part of this invention. The molecular ratio of sulfone to bis-phenol can be varied somewhat but should not exceed one mole sulfone to one mole bis-phenol. However, as low as 0.75 mole sulfone may be used per mole of bis-phenol. The total quantity of formaldehyde may be varied slightly i.e., from about 1.5 to 2 moles per mole of sulfone or bis-phenol. The formaldehyde present in each of the three condensation stages may vary from 0.5 to 0.7 mole of formaldehyde based on each mole of either the bis-phenol or the sulfone. The formaldehyde is used preferably as formalin, which is an approximately 37% aqueous formaldehyde solution although it may be used in one of its polymeric forms ULl'lltMll ttuuavr 4 such as paraformaldehyde, trioxane, etc. Additionally formula which covers the various condensation products compounds liberating formaldehyde upon heating may which are obtained as a result of the condensation be used, such as monomethylol dimethyl hydantoin. reaction.

In order to determine whether the final condensation The product when recovered and buffered to a pH of product is suitable for use in tanning, it should satisfy 5 about 3.2 is in an aqueous solution of a concentration the following criteria: it should be completely free from from about 50 to 60% by weight and may be used directly any excess formaldehyde, easily soluble in water and in tanning procedures. If desired, the product may be form a clear solution therein, it should be soluble in a isolated e.g., by drum or spray drying or by salting out 5% acetic acid solution and be immediately precipitated the solid material e.g., with heavy brine. upon addition to a sodium chloride solution or 10 As indicated previously the product is an excellent precipitated after a few minutes by addition to a 5% synthetic tanning agent with unlimited stability in solusodium chloride solution. The reaction may be repretion form. It can be used as a retanning agent for chrome sented as follows: retan, as a bleaching agent, as a dispersing agent in no on no R: 12 on ECHO 0 X035 S o'x three stage condensation Sulfone Bis-phenol disulfonlc acid salt HO OH HO R: R OH l I so X0=s 0 soar in n Condensation product in which R is H or CH;,, R is CH;, or --CH CH vegetable tanning processes, for shrunken grain tanning R is --H or-CH X is a metal from the alkaline processes and for many other purposes. On chrome group, or ammonium, and n is an integer between about retan, the product gives a full, plump leather with a soft 3 and 4. The degree of sulfonation indicated in the touch and good hand.

preceding structural formula of the bis-phenol and of For a fuller understanding of the present invention the final condensation product by the presence of two reference is made to the following examples which are SO X groups per bis-phenol unit represents an average given for purposes of illustration only and are not to be since some molecules may have only one SO X group construed in a limiting sense. Unless otherwise stated while others may have two or more. all parts are given by weight.

Since phenol and ortho, meta, and para cresols may 40 be used alone or in admixture with each other in varying proportions to form the sulfone reactant, the sulfone A. Preparation of sulfone.To 100 parts of crude may be represented by the following configurations as phenol were added parts of 100% sulfuric acid. The well as mixtures thereof although it is understood that resulting mixture was stirred for 2 hours at 100 C. these are not all of the possible sulfones that can be 45 Then 10 parts of chlorobenzene were added and the temderived from the preceding phenol and cresols: perature raised gradually to 150 C. The water from HO OH benzene) was removed by addition of 30 parts water CH3 OH OH followed by distillation. The resulting dihydroxy diphenyl sulfone was in the form of a wet paste having a conso CH so centration of 70-75% by weight.

B. Preparation of the sulfonated bis-phen0l.-To 100 parts of 2,2 bis (para hydroxy phenyl) propane were Example I 50 hydroxide solution and the remaining solvent (chloro- H0 0H OH HO OH; OH OH added 80 parts of 98% sulfuric acid. This mixture was heated at a temperature of 110 C. for 5 hours. The 0 so so,- resulting product was then diluted with 150 parts of water and neutralized with 90 parts of a 45% sodium hydroxide Hence, the sulfone portion of the final condensation solution. product may be derived from any of the above sulfones C. Condensation with formaldehyde.The entire quanor mixtures thereof. This is demonstrated, for instance, tities of the products of A and B, i.e., the sulfone and by Example III in which bis-phenol is condensed with a bis-phenol were admixed, the pH adjusted to 8 by addisulfone mixture in which the sulfones are (1) dihydroxy tion of sodium hydroxide, and 20 parts of a 37% by diphenyl sulfone and (2) a mixture of isomeric cresyl weight aqueous solution of formaldehyde added. This sulfones. Also the bis-phenol disulfonic acid salt may mixture was refluxed for 4 hours. Then lactic acid was be considered a mixture of salts since the degree of added to adjust the pH to about 7.0, 20 parts more of sulfonation previously indicated represents an average formaldehyde added and the mixture refluxed for 3 hours.

value. Also, as stated before, the condensation product Thereafter 20 parts of lactic acid were added to adjust is actually a mixture of polymers of different chain lengths. the pH to about 4.5 and 20 more parts of formaldehyde It is obvious therefore, that the syntan molecule need not introduced. Reflux was carried out for 5 additional be identical in each of its units as represented by the hours. The pH was finally adjusted with 60 parts glycolic formula for the condensation product in the preceding acid to about 3.2. The product was an aqueous soluequation. Hence, the above formula represents a basic tion containing about 52% solids.

the reaction was thereby azeotropically removed with the HO O chlorobenzene during heating for 5 hours. The reaction mass was then neutralized with 25 parts of a 40% sodium 0H so Example II A. Preparation of the sulfone.A mixture of 50 parts cresol and 50 parts phenol was prepared. The cresol was a technical grade containing 54% meta cresol, 29% para cresol and the remainder other phenols including ortho cresol and xylenols. To this mixture was added 50 parts of 100% sulfuric acid. This new mixture was stirred for one hour at a temperature of 110 C. Chlorobenzene was added, and the temperature was raised to 150 C. thereby removing azeotropically the water formed during reaction. After heating for 4 hours, the reaction mass was cooled and neutralized with a dilute sodium hydroxide solution. The solvent was removed by addition of 40 parts of water and distillation. In this manner, a mixed sulfone in the form of a 60 to 65% by weight of a wet paste was obtained.

B. Preparation of the bis-phenoL-To 120 parts of 2,2 bis (para hydroxy pheny-l) propane was added 85 parts of 100% sulfuric acid. Stirring at a temperature of 110 C. for 4 hours was carried out. The product was diluted with 150 parts of water and neutralized with 90 parts of a 45% sodium hydroxide solution.

C. Condensation with formaldehyde-60 parts of the sulfone of part A were admixed with 20 parts of the bisphenol of part B. Thereafter condensation was carried out in the same manner as indicated in Example I, part C.

Example III This example is directed to a condensation product obtained from a mixture of sulfones.

A. Preparation of sulfne.The sulfones of Examples IA and HA were prepared and admixed in a weight ratio of 1:1. This mixture was partially neutralized with sodium hydroxide to a pH of 4.0 to 5.0.

B. Preparation of bis-phenoL-The bis-phenol of Example IB was prepared and partially neutralized with sodium hydroxide to a pH of 4.0 to 5.0.

C. Condensation with formaldehyde.60 parts of the product of part A and 22 parts of the product of part B were mixed together, the pH being about 4.5. To this mixture of weakly acid intermediates, 25' parts of formaldehyde were added and the mixture refluxed for 5 hours. The product was then neutralized with sodium hydroxide to a pH of 7.0. Then 22 additional parts of formaldebyde were added and reflux carried out for 4 hours. The pH was then adjusted to 8.0 with sodium hydroxide, 22 more parts of formaldehyde added and the mixture refluxed for a final 4 hours. The pH was adjusted to 3.4 with 12 parts glycolic acid.

The following examples illustrate the use of our novel synthetic tanning agents in treatment of leather.

Example IV This example is directed to a synthetic retan of leather with our novel agent.

Chrome tanned cowhides were washed for 30 minutes and neutralized with 1% ammonium bicarbonate, and washed again for a few minutes. The hides were placed in a drum containing 300% water based on the shaved (blue) weight of the hides and 12% by weight thereof of the product from Example I was added. The drum was then run for 2 hours and the hides washed, fatliquored and finished in the usual manner. A very plump and pliable piece of leather resulted with a fast and smooth grain and having a very high tensile and stitch tear strength.

Example V This example is directed to shrunken grain tanning.

Pickled calfskins were placed in a drum containing 120 water based on the pickled weight of the skins and treated with 20% by weight of the skins of the synthetic tanning agent of Example I. The drum was rotated for 2 hours. The synthetic tanning agent was taken up very well by the skins and the grain was shrunken satisfactorily. The

exhausted liquor was drained and the skins washed in 300% water bath based on the weight of the skins for five minutes. To a new bath containing 100% water and the skins, 8% by weight of the skins of Tanolin R (a chrome tanning agent which is a dry chrome salt 33% basicity and 25% Cr O content) was added to complete the tanning and the drum rotated for 5 hours. A solution of 1% ammonium bicarbonate dissolved in 10% water was added slowly during /2 hour. The drum was rotated for an additional hour. The skins were thereafter horsed for 48 hours, then washed, neutralized, dried, fat-liquored and finished in the usual manner. The resulting leather was found to be very soft with a nice pattern.

Example VI Pickled calfskins were treated in a tanning drum containing 100% water with 10% by weight of the skins of the product from Example I for 2 hours in order to shrink the grain. The liquor was drained and the hides washed with 500% water for 5 minutes. In a new bath containing 100% water, 5% of a cationic aminoplast resin (50% solids base) was added to fix the shrunken pattern and the drum rotated for 1 hour. The liquor was drained and the skins washed for 5 minutes with 500% water. In a new bath the skins were chrome tanned with 10% Tanolin R to complete the tanning. The initial pH of the chrome bath was 3.4. After 4 hours the chrome solution which showed now a pH of 2.5 was neutralized slowly with 1% NH HCO solution and the drum rotated for an additional hour. The final pH was 4.0. The calfskins were finished in the usual manner. The shrunken grain pattern was fixed very well. The leather was firm, but not harsh. Its firmness naturally can be adjusted if desired by variations in fat-liquoring.

Such expressions as percent water, percent Tanolin R, etc., as used in the last three examples, mean percent by weight of the skins in accordance with the practice in the art.

As the foregoing has demonstrated, novel synthetic tanning agents have been described which have been found to be superior to the prior art agents. It will be appreciated that various modifications can be made in this invention as described above and such are within the scope of the present invention as defined in the appended claims.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A process for obtaining synthetic tanning agents comprising mixing together from about 0.75 to one mole of at least one sulfone of the formula HO OH SOtwherein R is selected from the group consisting of H and CH with one mole of a disulfonic acid salt of a bis-phenol of the formula in which R is selected from the group consisting of 'CH andCH CH and R is selected from the group consisting of H and CH and which is sulfonated to an average degree of about between 75 and of the theoretical amount of the disulfonic acid salt and thereafter condensing the resulting mixture with from about 1.5 to 2 moles of formaldehyde in three stages by (1) reacting said mixture with from 0.5 to 0.7 mole of formaldehyde for about 4 to 5 hours in a weakly acid solution 8 having a pH of from about 4 to 5, thereafter (2) react- 9. As a synthetic tanning agent, a mixture of condensaing said mixture with from about 0.5 to 0.7 mole of tion products having the basic formula formaldehyde for about 2 to 4 hours in neutral solution in which R is selected from the group consisting of H and (3) finally reacting said mixture with from about 0.5 and CH R is selected from the group consisting of to 0.7 mole of formaldehyde for about 4 to 5 hours in CH and CH CH R is selected from the group a weakly basic solution having a pH of from about 8 to 9. consisting of H and CH X is selected from the 2. A process for obtaining synthetic tanning agents group consisting of alkali metals and ammonium, n reprecomprising mixing together from about 0.75 to one mole sents an average positive integer between about 3 and 4 of at least one sulfone of the formula and the degree of sulfonation of said agent being an average of about 75% to 85% based upon the bis-phenol R R disulfonic acid salt portion of the molecule. HO OH 10. The synthetic tanning agent of claim 9 in which both substituents R are H, both substituents R are s02 CH and both substituents R are H.

11. The synthetic tanning agent of claim 9 in which both substituents R are CH both substituents R are CH and both substituents R are H.

h l t d fr th n t f H 3 2 g f g fi s gg g: z gg figg s ig fi of a 12. The synthetic tanning agent of claim 9 in which the formula one substituent R 18 H and the other is CH both p substituents R are CH and both substituents R are Ho R, R 13. The synthetic tanning agent of claim 9 in which R; said degree of sulfonation is about 80%.

14. The synthetic tanning agent of claim 9 in which the aromatic rings of the sulfone portion of the molecule are derived from a mixture of ortho, meta, and para cresols. in which R is selected from the group consisting of 15. The synthetic tanning agent of claim 9 in which CH andCH CH and R is selected from the group the sulfone portion of the molecule is derived from 2. consisting of H and CI-I and which is sulfonated t0 mixture of (1) di-hydroxy di-phenyl sulfone and (2) a an average degree of about between 75 and 80% of the mi tur f isomeric dicresyl ulfones, theoretical amount of the disulfonic acid salt and there- 16. A synthetic tanning agent comprising an aqueous after condensing the resulting mixture with ffoul about solution of a mixture of condensation products having 1.5 to 2 moles of formaldehyde in three stages by (1) the basic formula R on, HO OH 110- R! R OH '11 SOn- XOaS- SOaX R1 n reacting said mixture with from 0.5 to 0.7 mole of formin which R is selected from the group consisting of H aldehyde for about 4 to 5 hours in a weakly basic soluand CH R is selected from the group consisting of tion having a pH of from about 8 to 9, thereafter (2) re- CH and CH CH R is selected from the group conacting said mixture with from about 0.5 to 0.7 mole of sisting of H and CH X is selected from the group formaldehyde for about 2 to 4 hours in neutral Solut on consisting of alkali metals and ammonium, n represents and 3) finally reacting said mixture with from about 0.5 an average positive integer between about 3 and 4 and the t0 -7 mole of formaldehyde about 4 to 5 hours in a degree of sulfonation of said agent being an average of weakly acid solution having a pH from about 4 to 5. about 75 to 85% based upon the bis-phenol disulfonic 3. The process of claim 2 in which said bis-phenol is acid salt portion of the molecule. su a to an average degree of about 17. The synthetic tanning agent of claim 16 in which The Process of Claim 2 in which both substituents R said tanning agent is present in an amount of about 50 of said sulfone are H an a bis-Phenol is bis to by weight of the solution and said solution is (para hydroxy phenyl) propane. 60 bufiered to a pH of about 3.2.

5. The process of claim 2 in which both substituents R R f of said sulfone are CH and said bis-phenol is 2,2 bis 6 erences Cted the file of thls Patent (para hydroxy phenyl) propane. UNITED STATES PATENTS 6. The process of claim 2 in which one substituent R 1,988,985 of said sulfone is Hv and the other is CH3 and said 5 2,129,553 3 353 1 1 32 bis-phenol is 2,2 bis (para hydroxy phenyl) propane. 2,174,287 Guthke Sept 1939 7. The process of claim 2 in which the aromatic rings 2 268 091 Niederm;l1 1941 of said sulfone are derived from a mixture of ortho, meta, 2522569 Day et a1 t 1950 and para cresols and said bis-phenol is 2,2 bis (para hyn P droxy phenyl) propane. FOREIGN PATENTS 8. The process of claim 2 in W iClI; Said 8 E011; s a 518,858 Great Britain Mar. 8, 1940 mixture of (1) dihydroxy diphenyl sul one and (2 a dicresyl sulfone, the aromatic rings of which are derived OTHER REFERENCES from a mixture of ortho, meta, and para cresols and said Ser. No. 237,057, Greth (A.P.C.), published Apr. 20,

bis-phenol is 2,2 bis (para hydroxy phenyl) propane. 1943. 

16. A SYNTHETIC TANNING AGENT COMPRISING AN AQUEOUS SOLUTION OF A MIXTURE OF CONDENSATION PRODUCTS HAVING THE BASIC FORMULA 